they ascended to heaven in a cloud Their ascent to heaven is much like that of Jesus following His resurrection (Acts Acts 1:9; Rev. Rev. 12:5+) and that of the Church at the Rapture (1Th. 1Th. 4:17). Their ascent, having been resurrected from the dead, is part of the first resurrection:

Although the resurrection of the righteous is called first in Rev. Rev. 20:4+, it is not one event but embraces a series of resurrection events, Every man in his own order: Christ the first fruits; afterward they that are Christs at his coming (1Cor. 1Cor. 15:23). Under the single profile of the first resurrection, therefore, is to be comprehended the resurrection of Christ, the rapture-resurrection of church saints, and the resurrection of tribulation saints (such as the two witnesses of Rev. Rev. 11:1-19+). It also comprehends the resurrection of Old Testament saints at the end of the tribulation.2

their enemies saw them We are specifically told that their resurrection is seen by their enemies. Their resurrection is perhaps the greatest moment of their ministry since they manifest the power and promise of God: the power to overcome death and the promise to raise believers from the grave. This, their greatest and last testimony, is not ineffectual for it contributes to the fear of those who survive the coming earthquake and results in their apparent salvation.

Notes

1 Not only does the weight of external evidence favor ἤκουσαν [ēkousan] , but since the Seer constantly uses ἤκουσα [ēkousa] throughout the book (24 times), copyists were more likely to substitute ἤκουσα [ēkousa] for ἤκουσαν [ēkousan] than vice versa.Bruce M. Metzger, A Textual Commentary on the Greek New Testament (Stuttgart, Germany: Deutsche Bibelgesellschaft, 1994), 672.